During the construction of oil and gas wells, a borehole is drilled to depth, the drill string is removed, and casing is inserted. The annular space between the outside of the casing and the wall of the borehole is then conditioned for cementing by pumping conditioning fluid down the casing. The conditioning fluid flows radially outwardly from the bottom of the casing and passes upwardly through the annular space where it entrains debris and carries it to the surface. Finally, cement is pumped downwardly through the casing. The pumped cement squeezes radially outwardly from the bottom of the casing and passes upwardly into the annular space where the cement then sets.
Conventionally, a fill valve is disposed toward the downhole end of the casing. The fill valve prevents fluid from entering the casing from the borehole, but permits fluid (i.e., mud, conditioning fluid, cement, etc.) to flow from the casing into the borehole. The fill valve is normally incorporated in a float shoe or a float collar. The float shoe is fitted on the bottom of the casing, whereas the float collar is typically incorporated between two lengths of casing.
FIG. 1 illustrates a conventional float collar 10A of the prior art. The collar 10A includes a tubular housing 12 accommodating a fill valve 30 therein. The fill valve 30 has a valve member 36 that is generally mushroom shaped with a head biased upwardly against a valve seat 32 by a spring 38 circumjacent a stem of the valve member 36. A base 34 in the seat 32 supports the valve member 36 and the spring 38.
The interior 12 of the housing 12 has an annulus filled with high density cement 20 disposed therein. The cement 20 supports the fill valve 30 and has a passage 22 communicating with the fill valve 30. During use, mud, conditioning fluid, and cement can flow through the passage 22 and the fill valve 30, but fluid from the borehole is not permitted to pass uphole through the valve 30.
The float collar 10A is mounted with its box end 18 at the bottom of casing (not shown). The pin end 16 can attach to another extent of casing or tubular. Alternatively, a shoe 40 as in FIG. 2A with box thread 48 can thread to the pin end 16 of the collar 10A to form a float shoe. The shoe 40 includes cement 44 inside its end that defines a passage 46 for communicating with the float shoe.
During use as a float collar, the casing having the float collar 10A with the connected shoe 40 is run downhole in the wellbore. Once the casing is in position, mud is pumped down the casing. The mud flows through the fill valve 30 and then passes out the passage 46 in the shoe 40. The mud flowing from the bottom of the casing then travels upwardly through an annulus between the casing and the wellbore to carry debris to the surface. Typically, mud is passed through the fill valve 30 for several hours. Conditioning fluid (usually referred to as “spacer fluid”) is then pumped down the casing. The conditioning fluid helps remove the mud and contains chemicals that will help the cement adhere to the casing.
After conditioning is complete, a charge of cement is pumped down the casing between a top plug and a bottom plug. After the bottom plug seats on (or near) the upper surface 24 of the float collar 10A, increasing pressure is applied against the top plug until a burst disk in the bottom plug ruptures and permits the cement to flow downwardly into the float collar 10A. The pressure applied to the cement by the top plug is transmitted to the head of the valve member 36, which moves downwardly away from valve seat 32, thereby permitting the cement to pass through the fill valve 30 and out the float shoe 40.
When the top plug contacts the bottom plug, no further cement passes through the fill valve 30. Pressure is then released on the top plug, and the fill valve 30 inhibits cement from flowing upwardly back inside the casing. After the cement has set, the top plug, bottom plug, fill valve 30, annular cement 20 in the float collar 10A, annular cement 44 in the shoe 40, and any other cement below the shoe 40 is drilled out.
As noted above, a shoe 40 as in FIG. 2A can be mounted to a float collar 10A to run in the casing in the borehole. The shoe 40 in FIG. 2A has a conventional nose 44 of cement defining a central passage 46 for communicating fluid (e.g., mud, conditioning fluid, and cement) out of the nose 40. The cement 44 is used because it can be readily drilled out after cementing operations.
In some wellbores, various features of ledges, carvings, and irregularities in the borehole can hinder the running of the casing to the planned depth. To overcome these obstacles, a float shoe nose with a conical or eccentric shape is commonly used. The shape and the material of the nose are preferably of sufficient strength to overcome high loads, yet are easily drilled using a drill bit. Composite and aluminum materials have been used in the past for these types of noses on the end of the casing.
For example, FIG. 2B illustrates a composite nose 50 of the prior art for use on a float shoe 10B. As before, the float shoe 10B includes a tubular housing 12 accommodating a fill valve 30 therein. The interior 12 of the housing 12 has an annulus filled with high density cement 20 disposed therein to support the fill valve 30. The cement 20 has a passage 22 in which the fill valve 30 is mounted.
The nose 50 is constructed of a composite material having wear resistant and drillable characteristics. Typically, fiberglass or some other composite material is used for the nose 50. Because the nose 50 is composed of composite material, it can be given a conical, eccentric shape. In this way, the nose 50 not only serves to direct fluid, but the eccentric conical shape of the nose 50 can aid in run-in of the assembly by facilitating the passage of the assembly through the borehole.
At an upper end, the nose 50 fits into the housing 12 of the float shoe 10B and is attached with a threaded connection 16, 56. A central bore 52 of the nose 50 is aligned with the longitudinal bore 22 of the annular cement 20 in the interior 14 of the housing 12. The nose 50 can also include a side port or jet 54 for the passage of fluid from the longitudinal bore 52 to the borehole (not shown).
As another example, FIG. 2C illustrates an aluminum nose 60 of the prior art for use on a float shoe 10C. As before, the float shoe 10C includes a tubular housing 12 accommodating a fill valve 30 therein (here, two fill valves are shown). The interior 12 of the housing 12 has an annulus filled high density cement 20 disposed therein to support the fill valves 30. The cement 20 has a passage 22 in which the fill valves 30 are mounted.
Because the nose 60 is composed of aluminum, it can be given a conical or eccentric shape and may have external features, such as wear resistant nodules, ribs, or the like. In this way, the aluminum nose 60 not only serves to direct fluid, but the shape of the nose 60 and any external features can aid in the run-in of the assembly by facilitating the passage of the assembly through the borehole.
At an upper end, the nose 60 fits into the housing 12 of the float shoe 10C and is attached thereto with a threaded connection 16, 66. A central bore 62 of the nose 50 is aligned with the longitudinal bore 22 of the annular cement 20 in the interior 14 of the housing 12. The nose 60 can also include a side port or jet 64 for the passage of fluid from the longitudinal bore 62 to the borehole (not shown).
Although the composite and aluminum noses 50, 60 on float shoes can be effective, the cost of these materials can increase the overall equipment cost. Side ports or jets for the noses 50, 60 are fabricated by drilling ports at an angle, which adds additional machine work and increases product cost. In addition to higher costs, aluminum materials of an aluminum nose 60 may be more difficult to drill up than composite materials of a composite nose 50. Yet, the composite materials often break up into larger pieces that can obstruct the drilling assembly.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.